&#42 '''chmod''' has several input options. Using a + and an r, w, or x will add read, write, or execute permissions respectively to the given file. A - will take these away. The other system is a binary system in which there are permissions for the private user, the group, and the public given as 000 000 000 where each set of three 0's equals the group respectively. The first 0 in each group for reading permission, the second for writing, and the third for executing. Because it is binary 100 000 000 (permission for the private user to only read) will be written as 400 in the command line (after translating the binary to decimal where 100 = 4)